A representative secondary battery is a lithium secondary battery. For reduction of carbon dioxide emission, improvement of energy efficiency and utilization of natural energy have been required and in the field of transportation, for example, where internal-combustion engines are considered to be one of the main carbon dioxide emission sources, and in order to minimize the operation of the engines, the utilization of a secondary battery in an electric car, a hybrid car, etc., has been desired. Further, in utilization of natural energy such as wind power generation or solar photovoltaic power generation, there is a problem in temporal fluctuation of power supply and to overcome the problem, the use of a secondary battery as a leveling power source to store surplus power has been desired. As a secondary battery, a large scale secondary battery, which should have a large capacity and be able to be used even after repeated cycles of charge and discharge over a long period, is required. Although a lithium secondary battery has been broadly used as a power source for a cell phone or a notebook PC due to its higher energy density among commercially available batteries, as a very large amount of battery materials are required, if directed to such a large scale secondary battery, there will be a problem of reduction in lithium resources. Since lithium which is a rare metal is used in a large amount therein, the supply of such a rare metal is of concern.
A sodium secondary battery has been studied, which can resolve the supply problem of the battery materials. A sodium secondary battery comprises a positive electrode, into which sodium ions can be doped and dedoped, and a negative electrode, into which sodium ions can be doped and dedoped. A sodium secondary battery can be constituted of materials, which are abundant for supply and low-priced. Consequently, it has been expected that, once it is developed, a large scale secondary battery will become available for supply in large quantities.
While a carbonaceous material with a structure of high degree of graphitization such as graphite has come into practical use as a negative electrode active material in a lithium secondary battery, and application of the carbonaceous material to a negative electrode active material in a sodium secondary battery has been tried. However, being doped and dedoped with sodium ions into such a carbonaceous material are difficult, therefore it is very difficult to use the active material for a lithium secondary battery as is as described above in producing a sodium secondary battery. To overcome this problem, JP11-40156A proposes that lithium ions are injected together with sodium ions into graphite which is a negative electrode active material in a sodium secondary battery.